Blue-fluorescent water-soluble lens proteins were isolated from bovine lenses by gel-filtration and found associated mainly with alpha-crystallin. While more blue-fluorescent water-soluble proteins were present in cow lenses than in calf lenses, little blue fluorescence was observed in embryonic lens proteins. Water-insoluble, but urea-soluble lens proteins from cow lenses were more strongly blue-fluorescent than those from calf lenses. These blue-fluorescent proteins exhibited a fluorescence maximum at 410-420 nm and an excitation maximum at 340-360 nm. Bovine lenses also contained non-protein blue-fluorescent compounds of low molecular weight, whose fluorescence and excitation maxima were at 455 and 347 nm, respectively. The intensity of blue fluoresence in water-soluble lens proteins varied, depending upon the type of gel-filtration. When lens proteins were weakly blue-fluorescent, the addition of organic mercurials enhanced blue fluorescence and induced a partial dissociation of protein aggregates. All of the blue-fluorescent species, blue-fluorescent water-soluble and urea-soluble proteins and non-protein blue-fluorescent species, were found photosensitive to near ultraviolet light and chemically reducible by sodium hydrosulfite.